Tuberculosis lymphadenitis in Southwest Ethiopia: a community based cross-sectional study

This community-based cross sectional study was conducted from February to March 2009 in Gilgel Gibe Field Research area (Figure 1) which is located in Jimma Zone about 260 kilometers Southwest of Addis Ababa around the reservoir of Gilgel Gibe hydroelectric dam. The site consists of four districts (locally known as Woredas): Sokoru, Omo Nada, Tiro Afata and Qarsa. Two small towns and eight rural Kebeles (smallest administrative units), situated within 10 kilometers of the reservoir of the dam were selected as field research site by Jimma University in 2005. Since then, regular demographic and AIDS mortality surveillances have been undertaken by Jimma University in the research site. At the time of the study, the total population of the field research area was 50,156 individuals in 10,882 households.

At the time of the study the total number of individuals 15 years or older in the study area was 30,040. A questionnaire was prepared in Amharic (local language) to identify TB lymphadenitis suspects in the study area. Trained personnel with high school education visited each household. If the heads of the households were not available during the visit, the data collectors repeatedly visited the same household up to 3 times. Individuals were asked if they had noticed lumps and bumps in the neck, armpits or groin themselves. Only those that respond positively were considered suspects and asked to come the next day to a center to undergo FNA. At the center those TB lymphadenitis suspects were interviewed using a structured questionnaire including questions about his/her socio-demographic situation.

The FNA was performed by the study pathologists. The diagnosis of TB lymphadenitis was made when smear microscopy, culture and/or cytology suggested TB individually or in combination.

FNA was performed using a 22-gauge needle attached to a 10-cc syringe. The aspirates were macroscopically evaluated for caseation. Two smears were prepared from each aspirate and air dried on site. The remainder of the aspirate was washed into 1 ml physiological saline for culture and transported to Jimma University Specialized Hospital in a cold box. FNA samples were kept at −20°C till transported in cold box by postal system to Armauer Hansen Research Institute (AHRI) in Addis Ababa for culture. All samples were transported within a maximum of 5 days.

One slide of a smear was stained with the Ziehl-Neelsen method [7] and examined for the presence of AFB by an experienced laboratory technician. The second smear was stained with Wright stain and cytological analysis was done by the study pathologists at Jimma University. TB lymphadenitis diagnosis by cytology was made by observation of the presence of epitheloid cell granulomas and caseous necrosis with or without Langhan’s giant cells [8, 9].

At the AHRI, the FNA samples were processed by the standard N-acetyl L-cysteine (NALC)-NaOH method [10] and concentrated at 3000 × g for 15 minutes. The sediment was reconstituted to 2.5 ml with phosphate buffer pH 6.8, to make the inoculums for the cultures. Two Lowenstein-Jensen slants, one containing 0.75% glycerol and the other containing 0.6% pyruvate, were inoculated with the sediment and incubated at 37°C. Cultures were considered negative when no colonies were seen after 8 weeks of incubation.

All consenting TB lymphadenitis suspects were tested for HIV after counseling. Testing for HIV was done as per Ethiopian national guidelines. HIV screening was performed using the KHB test (Shanghai Kehua Bio-Engineering Ltd, Shanghai, China; 2008). A positive sample was retested using the STAT-PAK test (Chembio Diagnostic System Inc, Medford, NY, USA; 2008).

Data were double entered using Epi-data version 3.1(Epi-data, Norway, 2006). For analysis, the data were exported to SPSS version 15.0 statistical software (SPSS Inc. Chicago, 2007). Descriptive analysis was done for the socio-demographic variables and prevalence of TB lymphadenitis. Logistic regression was done to assess factors independently associated with TB lymphadenitis in terms of the crude odds ratio and its 95% confidence interval (CI). A p-value less than or equal to 0.05 was considered significant.

A total of 30,040 individuals 15 years or older in 10,882 households were screened for TB lymphadenitis. Complete data were available from 9 Kelebes (27,597 individuals 15 years or older) while one Kebele was excluded from analysis because of incomplete data. After interview 87 TB lymphadenitis suspects were identified. The mean age (±SD) of the suspects was 33.1 (±11.3) years. Most (72.4%) were women and married (81.6%). Thirty one (35.6%) lived in close contact with animals and 45 (53.5%) used to drink raw milk.

On the basis of FNA smear microscopy for AFB, cytology and culture 16 (18.4%) of the lymph nodes were diagnosed as tuberculous. Smears were positive in 2, culture in 6 and cytology in 13 of the suspects. The microscopic features of FNA cytology of the TB lymphadenitis showed epithelial histocytes with giant cells in 8 cases, epithelial histocytes with caseous necrosis in 2 cases and caseous necrosis alone in 3 cases. Three of these 16 cases were positive by both culture and FNA cytology. The mycobacteria isolated in 6 cases were identified as Mycobacterium tuberculosis based on RD typing. The remaining 10 cases that were negative on culture but positive on smear and/or cytomorphology were also considered to be tuberculous. The distribution of TB lymphadenitis cases per kebele is indicated in Table 1. The prevalence of TB lymphadenitis was 58.0 per 100,000 people (16/27,597) (95% CI 35.7-94.2). Other diagnosis of the lymph nodes include: reactive lymphadenitis (57), pyogenic lymphadenitis (6), benign mesenchymal neoplasia (6) and non-specific lymphadenitis (5).

TB lymphadenitis was more frequent in females (86.5 per 100,000) and age group 35–44 (90.4 per 100,000 people) followed by 45 years or older (71.9 per 100,000 people). The differences in the prevalence of TB lymphadenitis with respect to sex and age group were not statistically significant (Table 2). Other personal characteristics associated with TB lymphadenitis are described in Table 3. Only contact with a person with chronic cough was significantly associated with TB lymphadenitis (OR 5.58, 95% CI 1.23-25.43).

Lypmh node characteristics affecting positivity for tuberculous lymphadenitis are described in Table 4. Among the lymph nodes characteristics only caseous FNA samples were more likely to be from persons with TB lymphadenitis (OR 5.46, 95% CI 1.69-17.61).